There are three separate persons in the Godhead: God, the Eternal Father; his Son, Jesus Christ; and the Holy Ghost. We believe in each of them (A of F 1: 1). From latter-day revelation we learn that the Father and the Son have tangible bodies of flesh and bone and that the Holy Ghost is a personage of spirit, without flesh and bone (D&C 130: 22-23). These three persons are one in perfect unity and harmony of purpose and doctrine (John 17: 21-23; 2 Ne. 31: 21; 3 Ne. 11: 27, 36).
God the Father: It is generally the Father, or Elohim, who is referred to by the title God. He is called the Father because he is the father of our spirits (Mal. 2: 10; Num. 16: 22; 27: 16; Matt. 6: 9; Eph. 4: 6; Heb. 12: 9). God the Father is the supreme ruler of the universe. He is all powerful (Gen. 18: 14; Alma 26: 35; D&C 19: 1-3), all knowing (Matt. 6: 8; 2 Ne. 2: 24), and everywhere present through his Spirit (Ps. 139: 7-12; D&C 88: 7-13, 41). Mankind has a special relationship to God that sets man apart from all other created things: men and women are God's spirit children (Ps. 82: 6; 1 Jn. 3: 1-3; D&C 20: 17-18).
There are few recorded instances of God the Father appearing to or speaking to man. The scriptures say that he spoke to Adam and Eve (Moses 4: 14-31) and introduced Jesus Christ on several occasions (Matt. 3: 17; 17: 5; John 12: 28-29; 3 Ne. 11: 3-7). He appeared to Stephen (Acts 7: 55-56) and Joseph Smith (JS-H 1: 17). Later he appeared to both Joseph Smith and Sidney Rigdon (D&C 76: 20, 23). To those who love God and purify themselves before him, God sometimes grants the privilege of seeing and knowing for themselves that he is God (Matt. 5: 8; 3 Ne. 12: 8; D&C 76: 116-118; 93: 1).
My God, my God, why hast thou forsaken me? Mark 15: 34. These men are the servants of the most high God, Acts 16: 17. We are the offspring of God, Acts 17: 28-29. Thou shalt offer thy sacraments unto the Most High, D&C 59: 10-12. Enoch beheld the spirits that God had created, Moses 6: 36. Man of Holiness is his name, Moses 6: 57.
God the Son: The God known as Jehovah is the Son, Jesus Christ (Isa. 12: 2; 43: 11; 49: 26; 1 Cor. 10: 1-4; 1 Tim. 1: 1; Rev. 1: 8; 2 Ne. 22: 2). Jesus works under the direction of the Father and is in complete harmony with him. All mankind are his brothers and sisters, for he is the eldest of the spirit children of Elohim. Some scripture references refer to him by the word God. For example, the scripture says that "God created the heaven and the earth" (Gen. 1: 1), but it was actually Jesus who was the Creator under the direction of God the Father (John 1: 1-3, 10, 14; Heb. 1: 1-2).
The Lord identified himself as I AM, Ex. 3: 13-16. I am the Lord [Jehovah], and beside me there is no savior, Isa. 43: 11 (Isa. 45: 23). I am the light of the world, John 8: 12. Before Abraham was, I am, John 8: 58. The Lord shall minister among men in a tabernacle of clay, Mosiah 3: 5-10. Abinadi explained how Christ is the Father and the Son, Mosiah 15: 1-4 (Ether 3: 14). The Lord appeared to the brother of Jared, Ether 3. Listen to the words of Christ your Lord and your God, Moro. 8: 8. Jehovah is the judge of the quick and the dead, Moro. 10: 34. Jesus appeared to Joseph Smith and Sidney Rigdon, D&C 76: 20, 23. The Lord Jehovah appeared in the Kirtland Temple, D&C 110: 1-4. Jehovah spoke to Abraham, Abr. 1: 16-19. Jesus appeared to Joseph Smith, JS-H 1: 17.
God the Holy Ghost: The Holy Ghost is also a God and is called the Holy Spirit, the Spirit, and the Spirit of God, among other similar names and titles. With the aid of the Holy Ghost, man can know the will of God the Father and know that Jesus is the Christ (1 Cor. 12: 3).
The Holy Ghost will teach you what you should say, Luke 12: 12. The Holy Ghost is the Comforter, John 14: 26 (John 16: 7-15). Jesus gave commandments to the Apostles through the Holy Ghost, Acts 1: 2. The Holy Ghost bears witness of God and Christ, Acts 5: 29-32 (1 Cor. 12: 3). The Holy Ghost also is a witness to us, Heb. 10: 10-17. By the power of the Holy Ghost you may know the truth of all things, Moro. 10: 5. The Holy Ghost is the spirit of revelation, D&C 8: 2-3 (D&C 68: 4).